cgroup/v1: move cgroup.procs to cgroupControllerRWFiles var
cgroup/v1: move cgroup.procs to cgroupControllerRWFiles var

Currently the cgroup.procs knob is magically appended in the
getControllerRWFiles method. This makes it more explicit, and adds it
to the referenced const var cgroupControllerRWFiles directly.

coreos/rkt,alban/rkt,cab105/rkt,achanda/rkt,lucasallan/rkt,alban/rkt,lucasallan/rkt,cab105/rkt,rkt/rkt,kinvolk/rkt,coreos/rkt,achanda/rkt,ybubnov/rkt,intelsdi-x/rkt,shobhit85/rkt,kinvolk/rkt,jakon89/rkt,rkt/rkt,lucasallan/rkt,jonboulle/rkt,shobhit85/rkt,jakon89/rkt,dgonyeo/rkt,sstabellini/rkt,joshix/rkt,rkt/rkt,cab105/rkt,intelsdi-x/rkt,ybubnov/rkt,Shashwatsh/rkt,kinvolk/rkt,lucasallan/rkt,coreos/rkt,Shashwatsh/rkt,kinvolk/rkt,intelsdi-x/rkt,sstabellini/rkt,achanda/rkt,sstabellini/rkt,jonboulle/rkt,jakon89/rkt,ybubnov/rkt,Shashwatsh/rkt,joshix/rkt,dgonyeo/rkt,joshix/rkt,dgonyeo/rkt,shobhit85/rkt,joshix/rkt,alban/rkt,jonboulle/rkt,rkt/rkt